v0.2.3

• gridstack-extra.css
• add support of lodash.js
• add is_area_empty method
• nested grids
• add batch_update/commit methods
• add update method
• allow to override resizable/draggable options
• add disable/enable methods
• add get_cell_from_pixel (thanks to @juchi)
• AMD support
• fix nodes sorting
• improved touch devices support
• add always_show_resize_handle option
• minor fixes and improvements